The present invention relates generally to direct current (DC) constant current driver circuits. More particularly, this invention pertains to voltage and current limited constant current DC driver circuits.
Light emitting diodes (LEDs) provide light in response to receiving a DC current (assuming proper bias) and in proportion to the received DC current. Resistance of an LED light source fluctuates. Therefore, constant current driver circuits are preferred with LED based light sources. Underwriters Laboratories (UL) class II standards for LED driver circuits require that the driver circuit have an isolated output, pass a short circuit test, provide a controlled (i.e., limited) output voltage, and provide a constant current. Generally, UL class II LED driver circuits are also dimmable. That is, the magnitude of the constant output current may be varied by the driver circuit to match a target current, thereby matching a target brightness output level for the LED light source.